1. Field of the Invention
This invention relates to a control device for motor driven antennas used in vehicles.
2. Prior Art
In the conventional control device for motor driven antennas, the antenna position is mechanically calculated by an antenna drive system which is linked with gears to the antenna, and the control device controls the position of the antenna with the thus obtained values. For example, when the motor revolves 100 times, the device recognizes that the antenna has been extended 1 m, for instance. Further, the conventional device uses a limit switch system so that when the antenna is fully extended or retracted, the switch mechanically functions to open and close the motor circuit.
However, since the conventional device positions (extends and retracts) the antenna by using gears, in other words, the positioning of the antenna is made mechanically, it is not easy to position the antenna accurately. Further, in order to reduce the mechanical stress, the conventional device uses a mechanical clutch. Thus, since the conventional device uses mechanical limit switches and mechanical clutches, the overall structure tends to be complicated.
In addition to the above, since the conventional device contains mechanically abrasive portions, the reliability of the motor antenna is low, and it is very difficult to design a device small.